1. Field of Invention
The present invention relates to an ion source for use with analysis and discrimination of substance with dual ion mobility technology, which belongs to a technical field of safety inspection.
2. Description of Prior Art
The dual ion mobility spectrometer (dual IMS) can simultaneously detect molecules having positive and negative ion affinity, and thus can conduct detection of various types of substances, such as drugs and explosives. This characteristic enables a wide application of the dual IMS.
The conventional ion sources, however, are designed primarily for single IMS. Such ion sources, when applied to the dual IMS, will have noticeable shortcomings, such as a low ionization efficiency of sample molecules, a low effective utilization of ions, and unreasonable ion source structure.
Currently, some ion sources dedicated to the dual IMS have disadvantages, too. In U.S. Pat. No. 7,259,369B2, for example, sample molecules after ionization in an ionization chamber external to the system are carried by carrier gas into a quad-polar ion trap at the center of the dual IMS. Then, ions stored in the ion trap enter positive and negative ion drift tubes at both ends of the dual IMS, respectively, for further measurement.
The ion source in the above patent has the advantage of being not limited by ionization approach and source body shape, and can be any one of the existing ion sources, such as radioactive isotope, corona or laser. On the other hand, the ion source has disadvantage of a significant reduction of effective utilization of ion, since a larger number of ions are lost in the course of sample ions migrating from the ion source to the ion trap. Further, the separate ionization chamber adds to the volume and production cost of the IMS.
In addition, to improve ionization efficiency, ion cloud generated by a general radioactive source for IMS has a broad distribution range. As shown in FIG. 1, the ion cloud 12 generated by the tube-shaped Ni63 source 11 is distributed in a broad space along the direction of tube axis, and such distribution leads to a bad resolution for the IMS.